Illumination



Dec. 13, 1938.

H. I. DAY ET AL ILLUMINATION 7 Filed May 20, 1932 INVENTOR #419010 a fl/JWOATH MIR/Pr 1 DAY BYTHf/RATTORNEY% Pasta D5913, 193s 2,139,732

UNITED STATES PATENT OFFICE ILLUMINATION Harry 1. Day, Kew Gardens, and Harold D. Ellsworth, New York, N. Y., assignors to Gustavus T. Kirby, New York, N. Y.

Application May 20, 1932, Serial No. 612,408

22 Claims. (01. 176-122) This invention relates to illumination and more efiiciency even with incandescent lamps provided particularly to the production of a substantially with filters. white light by means of an electric discharge The present invention is based on the remarkthrough rarified gases, giving a banded spectrum. able discovery that under certain conditions In the past the so-called neon lights and simimonatomic gases, such as the rare inert gases lar methods of illumination by the passage of of the atmosphere, helium, argon, neon, krypton electricity through rarified gases in tubes have and xenon, and in some cases other monatomic achieved widespread success by reason of their gases, such as mercury, are transformed into a high illumination with low glare and by the fact condition where, instead of emitting their typithat such illumination is economical in operacal line spectrum, they emit a spectrum which tion. However, such lamps when used with the is handed and which in the case of .the rare rare monatomic gases have been open to very gases and their mixtures gives a light which has serious disadvantages because the light is colored approximately the spectral balance of north skyand cannot be used where a white or substanlight. The physical state f the gas atoms ortially white light is desired. The production of nuclei has not yet been determined, but since white lights permitting illuminating effects comthe gases behave-or seem to behave.as if they parable with those of sunlight or skylight has' had suddenly been transformed into diatomic required the use of incandescent lamps with 131- gases it is believed that some form of association ters and a resultant low eficiency' of illumination. or change in the electron orbits takes place which It has been proposed in the past tomix various permits a change in the rotational. state of the gases having bright lines in diiferent parts of atoms or molecules corresponding to that in dithe spectrum in such proportion that the light to atomic gases and therefore results in the emisthe eye appears white. However, the illuminasion of light of wave lengths evenly distributed tion, that is to say, the light reflected by. the through the spectrum in the form of broad bandsr parts illuminated with such devices, is in no way Since theexact nature of the change in the gas comparable to illumination by a true white light is not known, the gases when so altered will bebecause practically all of the radiation from the referred to in the specification and claims as light source is -in a few narrow lines in the associated gases. It should be understood, howspectrum, leaving large gaps from which no illuever, that the invention is in no sense limited to mination is obtained. the above theory and that the term associated 39 Various diatomic gases, such as nitrogen, cargases does not limit the invention to gases bon monoxide and the like, have been proposed where there has been an actual chemical union. cause 61- n p ymic gases exhibit the Thephenomenon of association on which, the phenomenon the so-called banded p fi present invention is based is a reversible one and that is to say, the light is .not emitted from a appears to be a property of the gas or gas mix- 35 few narrow lines but from ratherbroad bands. ture itself, since by suitable changes in the op- The stable diatomic gases produce, it is true, the erating condition of the lamps a non-associated banded spectrum, but the balance of the specmonatomic gas or mixtures can be transformed 'trum, that is to say, the proportions of the illuinto an associated gas and back again to the 40 mination from various zones, is not that remonatomic state.

quired for white light. In the case of certain When the gas or gas mixture has become assopolyatomic gases, such as certain hydrocarbons, ciated it retains this property untilsubjected to it is possible to obtain a fairly satisfactory white electrical and/or heat conditions resulting in reor substantially white light which exhibits a versal to the original or dissociated state or to banded spectrum, but these gases are not stable such other conditions which are sufficiently pow- 45 and no practically useful lamp can be made erful to result in a dissociation of the gas. While which contains them .unless they are constantly associated the gas may be pumped from one lamp renewed as, for example, in the so-called. Moore to another without any loss-of its characteristic lamp where. ingenious methods were evolved for property. a constant-supply of fresh polyatomic gases to' The association of monatomic gases is brought make up for-the losses due to decompositionin about by operating them for various periods, d the operation of the lamp. Such devices, how-. pending on the length of the tube'or lamp and ever,.are extremely complicated and expensive to on the current, at pressures lower than those operate and, except invery few instances, cannormally used in a lamp of the type and with not compete from'the standpoint 0i cost and current densities higher than those normally used and preferablyincluding the employment of electrodes which are active electron emitters.

The association, when observed by means of a spectroscope, begins by a gradual widening of the typical line spectrum of the monatomic gas into bands followed by the appearance of new lines in other parts of the spectrum which gradually merge into the band's, giving an excellent spectral balance. The association is more rapid. the greater the current density and the greater the electron emission and takes-longer with long, large tubes than with short, small tubes. The period of association will vary from a few minutes to many hours, depending on the choice of the electrical conditions. v

In the accompanying drawing we have shown examples of tube and electrode construction in which our invention may be embodied:

Fig. l-shows a tube in vertical elevation with one end and the contained electrode in vertical section.

Fig. 2 is a vertical section of another form of tube which may be used with the invention,

showing only one end, e. g., the same portion as electrode I3 is preferably first formed by drilling a cylinder from both ends, and leaving an integral web uncut within the cylinder. Into one end of this, the electrode I2 is secured, e. g., by

crimping or pressing the nickel to the electrode. A bead of glass It is preferably formed uponthe wire l2, and the electrode l3 and the. wire l2 are then inserted through a hole in the end of the bulb l2 until the bead I4 is well within the bulb. A further body of glass I 5 is then pulled up around the wire l2, and serves to weld the bead [4 to the bulb II. A body of cement IE1 is then placed over the bead l4, and a refractory sleeve I! is inserted into the bulb l I from the opposite end, and is pressed into the, cement, so that it is held, as shown in the drawing, in the desired relation to the electrode l3. The cement should sufficiently cover the wire '2 and the bottom of the electrode so as substantially to prevent discharge directly from the wire l2, and require all such discharge to occur at the surface of the electrode I 3.

In Fig. 2 is shown a modified form of the invention, in which the electrode BA is secured directly to the wire l2, and this may be sealed into the bulb I I exactly as has just been described. In this case, however, a sleeve ll! of mica, or other refractory material, surrounds the end of the electrode so as to protect the bulb l l against sputtering.

Apparently the phenomenon of association and its maintenance are influenced by the presence of certain elements. Thus certain substances, of which sodium is an example, appear to favor dissociation, presumably as dissociation catalysts and/r perhaps as poisons-for catalysts which may normally maintain the desired association. Like sodium, 'the other alkali metals in compounds in which they are sufliciently loosely bound may also favor dissociation. Thus, for example, it is not possible to obtain an association with a resultant white light in a tube or ordinary glass which contains alkalies a sufliciently active or loosely bound form toactras dissociation catalysts (or poison), and Ba gas already associated is introduced into such a tube it will rapidly reverse itself to the dissociated form. It is, therefore, necessary to use tubes of materials which are free from loosely bound alkalies. Thus, for example, the various grades of borosilicate glasses can be used eifectively as can quartz or other transparent materials free from dissociating catalysts. A preferred refractory borosilicate glass obtain- .able on the market under the trade-mark Pyrex, contains from 4 to per cent. of alkalies and about 12 per cent. of boronoxides. This contrasts with from to 18 per cent. of alkalies in ordinary lead or lime glasses. Some borosilicate glasses also contain a large amount of alkali metal oxides and are in that respect unsuitable. The phenomenon appears to depend also to some extent on the activity or looseness of chemical combination of the alkali in the particular glass for, of course, only the alkali which is sufiiciently loosely bound to be in an active condition influences the behavior of the gas. The phenomenon is, of course, one of contact and it is therefore only necessary to be assured that the wall of the tube or lamp actually contacting with the rare gas is free from a sufficient concentration of dissociating catalysts to prevent association of the gas. Therefore, an ordinary glass tube, if coated on the inside with a layer of a glass or other material free from dissociating catalysts, will operate satisfactorily. The amount of dissociation catalyst which may be present in the glass depends also to some extent on the internal diameter of the glass tubes. Of course, the larger the internal diameter, the smaller the surface of contact per unit volume of gas. The effect of dissociating catalysts can be partially compensated for by an increase in current density. Thus, as will be pointed out below, large tubes of glass containing a small amount of dissociation catalyst may be operated safely at current densities slightly less than those required for smaller tubes. Of course, when a quartz tube is used the banded spectrum which extends well into the ultra-violet will be transmitted in these regions to a much greater extent than when refractory borosilicate glass or other suitable glasses are employed. The spectral balance in the ultraviolet remains excellentand still shows a banded structure, so that certain uses where the ultraviolet radiatlon of normal sunlight is desired can be served by the modification of the present invention, using quartz tubes or tubes of other materials which are capable of passing the desired amount of ultra-violet radiation.

While the present invention is applicable to tubes of any reasonable length, the higher current density required taken together with the low pressure of gas needed requires very high voltages in long tubes even with electrodes which are very eflicient electron emitters. The present invention is, therefore, more particularly advanrequired with pure helium orwith mercury are, considerably higher than with the other monatomic gases, requiring in the case of helium crease somewhat, e. g., down to about-one and invention. The pressure of the gas for association and maintenance in the associatedstate in general-should be of the .order of 4 millimeters absolute, the best results being obtained at from 2 to 3 millimeters. Lower pressures may be used, of course, but troubles are more likely to be encountered with excessively low pressures due to electrode sputtering.

The current density required for association with gases other than pure helium is normally of the order of 2 milliamperes per square millimeter in a tube of 7 millimeters internal diameter.

With larger tubes the current density may dethree-quarters milliamperes. The lower current densities are applicable when electrodes are used which are emcient electron emitters, as apparently the electron stream plays some role in the association and much higher current densities are required where plain nickel electrodes are used without a coating of materials which are eflicient electron emitters. All of the well known electron emitters such as oxides of the alkaline earths may be used. An electrode coated with barium azide which is transformed into a particularly active barium compound in use has been found to be very suitable. I

The invention will be described in greater detail in connection with examples of typical lamps.

Example 1.-A 5 foot quartz or refractory borosilicate glass tube of 9 millimeters internal diameter is provided with nickel electrodes covered withv barium azide and insulated with a suitable may be used as electrode, and coated as described above. The internal diameter of the glass enclosing the electrode cylinder, should be about 20 millimeters. The tube is operated with an alternating current supply of 60 cycles providing somewhat by increasing the current density and wheni'ully associated gives a white light characterized by a very uniform banded spectrum.

The efficiency of the lamp is from one and onehalf-to four times that of an incandescent lamp with daylight filter and is from one-half to twothirds as great as with a neon lamp operated in the usual manner with a line spectrum at the customary pressures and current densities,

Example 2.-A 10 foot tube of quartz or Pyrex glass 9 millimeters internal diameter is bui t with electrodes of the same shape as described in Example 1 but coated with a mixture of barium in a short tube.

' responding to the frequency of the alternating or azide and radioactive material such as salts of radium or mesothorium. The lamp is filled with argon or a mixture of helium and argon in about equal proportions evacuated to a pressure of about 3 to 3.25 millimeters. with a striking voltage of about 5000 volts and will run with a steady voltage of from 3000 to 3200 volts, depending on the amount of radioactive material present in the electrodes, as the radioactive material emits the more copious stream of electrons and therefore permits the same current density with a lower voltage.

The supply may be 60 cycle alternating current or a direct current of the same voltage which may, if desired, be made pulsating by any suitable interrupter. It will be noted that the volt ages for a 10. foot tube are considerably less than double those required for a 5 foot tube because a considerable portion of the resistances of the tube is in the voltage drop from cathode to gas. This voltage drop is substantially constant with any given type of electrode irrespective of the length of the tube but, of course, in a long tube it forms a smaller percentage of the total resistance than From the standpoint of emciency per watt, therefore, there is some advantage in using longer tubes where the higher absolute voltages required do not become prohibitive in cost.- The use of radioactive or electronemitting materials on electrodes reduces, of

- course, to a considerable extent the voltage drop.

Example 3.- -A 10 foot "Pyrex tube of '7 to 9 millimeters diameter is wound in the form of a tight spiral and is provided with electrodes as described in Examples 1 and 2. Thetube is filled 35 with argon or a mixture of argon with from 5 to 10 percent. of krypton and xenon andabout 10 per cent. of neon. The helix is placed in the output circuit of the power tube of a singlesided television amplifier. The direct current voltage is adjusted to a point just below the voltage required for sieady operation. The amplifier is then put into operation and the tube started by a temporary surge of sumcient magnitude. The tube will then operate at the frequency, of the 45 modulation of the television electric impulses and .when viewed through a" scanning disk properly synchronized will reproduce the" picture televised in white light instead of the usual pink of the neon light television amplifier. 50

The lamps of the present invention have been described specifically in connection with ordinary illumination or in connection with television amplifiers, They can be used, of course, for any other purpose for which a lamp of the ordinary neon type is I suitable, an excellent qualityof white light; being provided and, as .the tube responds almost instantaneously to changes in voltage,'it may be used to-emit light in pulses corpulsating direct currents with which the tube or lamp is supplied. It should be noted, however,

that in the caseof-a pure alternating current the wave form of the lamp response is not a true sine wave. On the contrary, the waive shows a broad 5 peak with a delayed extinguishment. This makes it useful in applicat ons where flickering would changes applied'to it instantaneously.

For some purposes it is. desirable to produce a 7 lamp having a-limited portion operating at higher be serious with a light which follows the voltage light intensity than the' remainder of the lamp- This can be accomplished by using a lamp having a limited portion oi smaller cross section than the rest or the lamp tube. In the smallercross sec- The tube will start 5 tion the current density per square millimeter of gas cross section is, of course, greater than in the rest of the lamp and correspondingly the brightness of this particular portion is greater. Such a lamp is particularly effective for SDECtI'ODhOtOIXIa etry where a small light source is needed.

Having described the invention, what is claimed is: I

1. A lamp of the class described comprising a tube filled with an associated stable monatomic gas at a pressure not exceeding about 4 millimeters, and an electrode at each end of the tube, the interior of the tube being free from any amount of dissociating catalysts which would cause cumulative dissociation of the gas when operated with current densities of not less than about one and three quarters milliamperes per square millimeter.

2. A lamp of the class described, comprising a tube filled with an associated stable monatomic gas at a pressure not exceeding about 4 millimeters, but sufiicient to avoid objectionable electrodesputtering, and electrodes spaced'apart in said tube, the inner walls of the tube being free from any amount of dissociating catalysts which would cause cumulative dissociation of the gas when operated with current densities for which the tube is designed.

3. A lamp of the class described comprising a tube filled with an'associated stable rare gas of the atmosphere at a pressure not exceeding about 4 millimeters, and an electrode at each endof.

the tube, the interior of the tube being free from any amount of dissociating catalysts which would cause cumulative dissociation of the gas when operated with current densities of not less than about one and three quarters milliamperes per square millimeter.

4. A lamp of the class described comprising a tube filled with a stable rare gas of the atmosphere having an atomic weight greater than 4 at a pressure not exceeding about 4 millimeters, and an electrode at each end of the tube, the interior of the tube being free from any amount of dissociating catalystswhich would cause cumulative dissociation of the gas when operated with current densities of not less than about one and three quarters milliamperes per square millimeter.

5. A lamp according to claim 1 in which the electrodes are coated with active alkaline earth oxides.

6. A lamp according to claim 3 in which the electrodes are coated with active alkaline earth.

oxides.

7. A lamp according to claim 4 in which the electrodes are coated with active alkaline earth oxides.

8. A lamp'according to claim,1 in which the tube length does not exceed about 10 feet.

9.A lamp according to claim 1 in which the 11. A lamp according to claim 4 in which the tube is of glass having not more than about 5% alkali.

12. A method of producing light having the spectral balance of white light and having a banded spectrum which comprises subjecting a stable monatomic gas at a pressure not exceeding about-4 millimeters in a tube provided with electrodes at each end, and in the absence or any amount of dissociation catalyst which would cause cumulative dissociation of the gas in a discharge of the hereinafter specified current to an electric current having a density greater than about one and three quarters milliamperes per square millimeter of gas cross section until the line spectrum: of the monatomic gas has been changed into a band spectrum having substantially the spectral balance of white light.

13. A method of producing light having the spectral balance of white light and having a banded spectrum which comprises subjecting astable monatomic gas at a pressure not exceeding about 4 millimeters but suflicient to avoid objectionable sputtering, in a tube provided with spaced electrodes, and in the absence of any amount of dissociation catalysts as would cause cumulative dissociation of the gas in a discharge of the hereinafter specified current, to an electric current having a density greater than about 1% milliamperes per square millimeter of gas cross section until the line spectrum of the monatomic gas has been changed into a band spectrum having substantially the spectral balance,

greater than about one and three quarters milliamperes per square millimeter of gas cross section until the line spectrum of the rare gas of the atmosphere'has been changed into a band spectrum having substantially the spectral balance of white light.

' 15. A method or producing light having the spectral balance of white light and having a bandedspectrum which comprises subjecting a stable rare gas of the atmosphere havingan'atomic weight greater than 4 at a pressure not exceed ing about'4 millimeters in a tube provided with electrodes at each end, and inthe absence of any amount ofdissociation catalyst which would cause cumulative dissociation of the gas in a discharge of the hereinafter specified current to an electric. current having a density greater than about one and three quarters milliamperes per square millimeter of gas cross section until the line spectrum of the rare gas of the atmosphere having an atomic weight greater than 4 has been ,changed into aband spectrum having substantially the spectral balance of white light.

16,- Amethod of illuminating by a light having substantially the spectral balance of north skylight and a banded spectrum which comprises operating a stable rare gas lamp containing an associated rare gas at a pressure not greater than about 4 millimeters .by means of an electric currenthaving a current density of not less than one and three quarters milliamperes per square millimeter of gas cross section, arid-in the absence of.

any amount of dissociation catalysts which would result in cumulative dissociation of the associated gas and production of a line spectrum in place of the banded spectrum.

17. A method of whiteli'ght illumination with a banded'spectrum which comprises passing an electrical discharge between electrodes in an associated rare gas at a pressure not greater than 7 gas to give it the capacity of glowing with a about 4 millimeters, .but sufllcie nt to avoid electrode sputtering and in' the absence of any a the rare gas is a mixture of helium and argon.

20. The method oil treating a stable monatomic white light under an electrical discharge which comprises subjecting it to a preliminary electrical'discharge treatment in a container, the inner wall of which is substantially tree fromfree and loosely combined alkali at a pressure not substantially greater than 4 mm. mercury pressure and a current density of at least about 1% m. a. per

square mm. cross section of the gaseous discharge path until the characteristic colored discharge of the gas is converted to an approximately white 810w.

21.' An artiflclally'modifled gas of the zero group of the periodic table, being associated so as to exhibit a substantially continuous banded spectrum under excitation by an electrical discharge, and said gas being stable at a pressure not ex ceeding about 4 millimeters under an electrical discharge of more than about one and threequarters milliamperes per square millimeter in the absence of dissociating catalysts.

22. The combination in a gas discharge lighting apparatus of a tube having electrodes for passage ofcurrent therethrough, a gas filling in said.

tube oi an associated gas of the zero group of the periodic table, at a pressure not exceeding about 4 millimeters, and means for supplying to the tube during operation a current not less than one and three-quarters milliamperes per square centimeter oi cross section of the gas discharge path,-

the interior of said tube being free 'from any amount 01' dissociating catalyst which would cause cumulative dissociation of the gas filling during operation from said current source.

HARRY I. DAY. HAROLD D. ELLSWORTH. 

